docs: def get_page_ids_by_slug(self, slug):
          """Return all page's id matching the given slug.
          This function also returns pages that have an old slug
          that match.
  
          :param slug: the wanted slug.
          """
          ids = self.filter(type='slug', body=slug).values('page_id').annotate(
              max_creation_date=Max('creation_date')
          )
          return [content['page_id'] for content in ids]